A collection of activities and demonstrations focusing on various aspects of the human immunodeficiency virus (HIV) life cycle. They are designed to be completed individually or as part of the series...

A hands-on activity in which students construct models of sickle-cell hemoglobin fibers inside red blood cells to illustrate how changes in the structure of a protein can affect cell shape. Students are then asked to relate these changes to disease symptoms. Also available in Spanish.

(1 min 8 sec) Once the structure of DNA was discovered, the next challenge was determining how the sequence of letters coded for the 20 amino acids. In theory, one or two letters can only code for 4 or 16 amino acids, respectively. A scheme using three letters, a triplet code, is the minimum necessary to encode for all the amino acids.

(1 min 44 sec) DNA is tightly packed in the nucleus of every cell. DNA wraps around special proteins called histones, which form loops of DNA called nucleosomes. These nucleosomes coil and stack together to form fibers called chromatin. Chromatin in turn forms larger loops and coils to form chromosomes.